1. Field of the Invention
The present invention relates generally to transport systems and methods for conveying articles along a conveyance path, and in some embodiments to conveying semiconductor substrates, or the like, in a fabrication facility.
2. Description of Related Art
Transport systems are widely employed in industrial manufacturing facilities to convey articles between work stations. Originally, these systems were manual and workers moved articles by hand or by cart. Modern factories have developed specialized equipment to convey articles automatically. In particular, semiconductor fabrication facilities currently use automated transport systems to move semiconductor wafers during the manufacturing process. Typically, a batch of wafers may be conveyed together in a container known as a Front Opening Unified Pod (FOUP). Semiconductor wafer manufacturers have sought to increase manufacturing productivity by using transport systems that quickly and efficiently convey wafers from machine to machine without exposing the wafers to excessive contamination, excessive vibration, or excessive acceleration and deceleration forces. One problem with existing transport systems used in the semiconductor manufacturing industry is the difficulty of changing or turning the direction of conveyance of an article, such as a FOUP, without momentarily stopping its forward motion. This wait leads to a bottleneck that limits the throughput and efficiency of such transport systems.
FIG. 1A illustrates a top view of a prior art transport cornering system. This system comprises a conveyor 110 including a belt 111 and a belt 112, and a conveyor 120 including a belt 121 and a belt 122. This system also comprises a turntable 130 configured to receive an article 140 from conveyor 110, rotate the article 140, and deliver the article 140 to conveyor 120. The turntable 130 comprises a belt 131 and a belt 132 on either side of the turntable 130, and an axis of rotation 133. A corner region 160 is shown magnified in FIG. 1B, FIG. 1C, and FIG. 1D to show the turntable 130 in successive stages of rotation as it delivers the article 140 from conveyor 110 to conveyor 120. The conveyor 110 uses the belt 111 and the belt 112 to transport the article 140 toward the turntable 130, where the article 140 is turned and delivered to the conveyor 120. The axis of rotation 133 is typically disposed between the belt 131 and the belt 132 on the turntable 130. Thus, a conveyance path of the article 140 passes through the axis of rotation 133.
When the article 140 reaches the corner region 160 and is approximately centered over the axis of rotation 133, the article 140 typically stops while the turntable 130 rotates to position the article 140 such that it may be delivered to the conveyor 120. The turntable 130 typically has a capacity to carry only one article 140 at a given time. The distance traveled per unit time by the article 140 through the corner region 160 is typically lower than the distance traveled per unit time by the article 140 over the conveyor 110 or the conveyor 120. To compensate for this, space is allocated between adjacent articles 140 on conveyors 110 and 120. As a result, the corner region 160 typically becomes a bottleneck in a transport system. Therefore, there is a need for improved systems and methods for changing or turning the direction of conveyance of articles in manufacturing facilities.